Most production oil wells contain a well casing within which a production tubing string is positioned. The production tubing string serves as both a means to easily insert and remove a pump rod and also provides a conduit for the extraction of oil and fluids from the well. Typically production tubing strings are held within the well casing through the use of a variety of flanges, hangers and other types of devices that tightly seal the well casing allowing fluids to escape or be removed by way of the production tubing string only.
In many cases an oil reserve or pocket is under considerable underground pressure. Once a well has been drilled, the static pressure to which underground oil is subjected often forces oil upwardly through the well. It is therefore important for conservation, safety and environmental reasons to ensure that there are safe and reliable methods of closing off both the well casing and the production tubing string to prevent the unwanted or accidental spillage of oil or other fluids from the well. In the case of the production tubing string, manually actuated valves or similar structures, often referred to as blow-out preventers, have been developed specifically for this purpose. However, such devices tend to be large, difficult or slow to engage and must be fastened separately to the wellhead making them prone to leakage. The prior devices also offer little assistance in instances where a pump rod breaks near its top, or where the rod has been removed from the production tubing string. In cases of pump rod removal or failure, others have proposed a variety of different methods and devices to seal off the well. These include bolting a flange over the top of the production tubing string and the use of large gate valves mounted in the production tubing string. The inherent short comings with these prior art devices include their inability to operate automatically in the event that a pump rod breaks when a technician is not readily available to shut down the well.
Furthermore, devices that have been proposed and used by others have tended to be large and cumbersome and must be bolted or screwed to the production tubing string. The connection of such devices to the production tubing string results in a wellhead of considerable height and weight. Traditionally such wellheads have been referred to as "Christmas trees" due to their size and the fact that there are usually a large number of elements pointing outwardly from various parts of the tubing string and the components mounted thereon. The servicing of oil wells having such "Christmas trees" attached to their production strings tends to be both complex and time consuming. In addition, with the bolting or screwing together of a large number of component parts, leaking at each junction is often a problem. Where a well casing is inclined or slanted, the considerable weight of these additional devices can place a significant degree of torque upon the various connections, sometimes resulting in failures or stress fracturing.
It has also been known to utilize rotators to slowly rotate the production tubing string in a well as a means to more evenly distribute pump rod wear on the internal surface of the tubing string to extend its life. However, heretofore such rotators have added further to the complexity, height and weight of the components mounted on the wellhead. Difficulties with leakage at joints, added height and weight, and increased torque in slanted wells are even more pronounced when such rotators are utilized.